Please follow the steps below to solve this problem.
Firstly, check the connection status. The instruction is shown in the following link.
Restart the device, whether it is a computer, cellular phone, or mobile phone, and then start the application.
Change the network protocol setting from TCP to UDP, or from UDP to TCP, depending on which one was the original option in the application.
When you are unable to make/ receive phone calls from the application, it may be because of the network block, which frequently occurs locally, or simply because of the system constraint from the insufficient call balance.
- Check the Available Balance:
Firstly, check your credit balance to see if there're credits available to make phone calls.
- Test the Connection Status:
The instruction is shown in the link below.
- Restart the Internet Router:
It may fix the issue to restart the internet provider's router computer and try again.
- Change the Internet Protocol in the Application:
Change the internet protocol or the transport type from UDP to TCP, or vice versa, depending on which one was the initial option.
Instructions on how to change the UDP/ TCP settings for:
- Check for the Firewall Blocking Port
Make sure that the next ports are open in the firewall of your computer.
Port 5060 TCP and UDP for the messaging called SIP.
Ports UDP 16384: 32768 to allow the RTP traffic for the audio streams.